The free acid of compound 4-((3-(4-cyclohexylpiperazin-1-yl)-6-oxo-6H-anthra[1,9-cd]isoxazol-5-yl)amino)benzoic acid (“Compound 701”) and its pharmaceutical composition are known in US Patent Application No. 20110301133 A1 (corresponding PCT Patent Application, WO2009/067197, which is hereby incorporated by reference) and has the following chemical structure:

Compound 701, and the physiologically acceptable salts thereof, have valuable pharmacological properties. Compound 701 is a receptor tyrosine kinase inhibitor, particularly a potent NGF receptor TrkA inhibitor which, by virtue of its pharmacological properties, may be used, for examples, for the treatment and/or prevention of acute and chronic pain, cancer, restenosis, atherosclerosis, psoriasis, thrombosis, skin diseases, inflammation, inflammation related diseases, or a disease, disorder or injury relating to dysmyelination or demyelination. Other possible therapeutic applications can be found in WO2009/067197, the contents of which are hereby referred to.
Due to the limited solubility of the free acid Compound 701, it is very difficult to achieve practical oral bioavailability in the in-vivo systems, for example, in rat. Salt formation has been widely used in the art to improve lipophilic, water solubility and/or oral bioavailability, among other issues in the industry. However, it is problematic and huge challenge for selection and testing of the enormous numbers of possible salt forms in practice, since Compound 701 is zwitterionic molecule, there are vast amount of counterions and/or molecules that could form salts or co-crystals with Compound 701 and they can be from either (i) anionic counter-ions, for examples, acetate, benzoate, bicarbonate, bisulfite, norate, bromide, carbonate, chloride, citrate, formate, fumerate, glcuconate, glucuronate, hydrochloride, malate, nitrate, phosphate, salicylate, succinate and tartrate; (ii) cationic counter-ions, for examples, ammonium, piperazine, diethlyamine, diethanolamine, imidazole, diethylammonium, ethylenediamine, betaine, lithium, sodium, potassium, calcium, magnesium, aluminum, zinc, bismuth and stonium; or (iii) zwitterionic molecules, for examples, glycine, bicine, tricine, sulfamic acid, lysergic acid, and psilocybin. Furthermore, each salt or co-crystal forms may form various polymorphs with various degrees of physicochemical properties in terms of, for examples, solubility, stability, and oral bioavailability, it is therefore problematic and huge challenge in practice.
Another aspect which is important in drug development is that the active substance should have the most stable possible crystalline morphology for the pharmaceutical quality of a medicinal formulation. If this is not the case, the morphology of the active substance may change in certain circumstances under the conditions of manufacture of the preparation. Such a change may in turn affect the reproducibility of the manufacturing process and thus lead to final formulations which do not meet the high quality requirements imposed on pharmaceutical formulations. To this extent it should generally be borne in mind that any change to the solid state of a pharmaceutical composition which can improve its physical and chemical stability gives a significant advantage over less stable forms of the same drug.